Electrode system for cathode ray tubes



May 28, 1940. H. KNIEPKAMP 2,202,588

ELECTRODE SYSTEM FOR CATHODE RAY TUBES Filed June 22, 195e INVENToRHEINRICH KN/EPKAMP .c fpm/LQ ATTORNEYS Patented May 28, 1940 UNITEDSTATES PATENT OFFICE ELECTRODE SYSTEM FOR, CATHODE RAY TUBES ApplicationJune 22, 1938, Serial No. 215,099 In Germany June 23, 1937 2 Claims.

Electrode assemblies for cathode ray tubes comprise as a rule quite anumber of electrodes serving for various purposes such as electronemission, acceleration of the emitted charge carriers, focusing thereofand the deflection of the cathode ray pencil. The assembling and thesupporting of these electrodes is diiiicult and requires a good deal ofprecision of workmanship. The chief demand is that the electrodes shouldbe J exactly centered. While this is a task in itself, there is anotherdiiculty in the electrode systems heretofore employed in which at leasta part of the electrodes consists of sheet material. These sheets beingof fairly large area and size are subd ject to warping when heated foroutgassing. No matter how carefully the electrode system has beenadjusted and alined, dissymmetry will often arise as a result, which mayproduce annoying n disturbances during the actual operation of thecathode ray tube.

Now, these drawbacks are avoided by the present invention. According tothe invention, at least those electrodes contained in a cathode ray ,Vtube which are substantially unloaded are made from graphite` Thismaterial offers the advantage that it will not warp when subjected to anoutgassing treatment, in fact, it will perfectly preserve its shape. Atthe same time, it is readily worked, for it can be fashioned in a lathe,for example, into a perfectly cylindrical or coneshaped body. Thisadvantage is not present where the electrodes are made of sheet or platematerial as heretofore customary. In the working of solid metal withturning or similar tools, "o the resulting thickness of the electrodebody will always be comparatively great, and as a result the electrodeis heavy. If low-weight electrodes are desired, they must be bent out ofsheet material, and this is always attended with a certain 'a lack ofprecision. In the making of electrodes from graphitic material, thedifficulty of undue weight is absent since this material has a very lowspecific gravity. Hence, comparative heavir ness in dimension is nodisadvantage and is La permissible without the electrode system becomingunduly heavy as a result.

Outgassing of graphitic electrodes such as those here disclosediseffected by the application of heating from the outside while the tubeis still "0 connected to the evacuating pump. In order to save the glassenvelope of the vessel or tube, the heating usually is not pushed beyondthe 400- degree mark. In fact, this outgassing temperature is perfectlyadequate inasmuch as the unloaded or but feebly loaded electrodes inopera- (Cl. Z50-162) tion will never be heated to such high temperaturesso that whatever gases may stay occluded therein will be readily keptinside the graphite. However, it is also quite readily possible tooutgas graphite by the use of high-frequency currents. In this case itis advisable to coat the graphite with a poor heat radiation layer inorder to prevent strong heat radiation.

In the drawing,

Figures 1 and 6 show alternate forms of assembled cathode ray tubeelectrodes constructed in accordance with this invention, and

Figures 2 through 5 and 7 through 10 show various modified forms ofelectrodes.

Referring to Figure 1, element I denotes a press or squash whichsupports an electrode system comprising a cathode 2, an acceleratorelectrode, an anode 4 and two deflector plates 5 and 6. The entireassembly is carried by four metallic rods 1, 8, 20, 2l, which are sealedin the press I. The 0 indirectly heated cathode 2, which is coated atits end 9 with electron-emissive substance, is surrounded by a Wehneltcylinder or shield IIJ made of graphite. This shield is borne upon amica disc I I, the latter being secured, in turn, upon the support rods'I, 8, 20 and 2|. The accelerator electrode 3, which also consists ofgraphite, is insulated from the shield III and spaced apart therefrom bytwo annular ceramic bodies I2 and I3. Two similar elements I4 and I5(also of ceramic) are interposed between the accelerator electrode 3 andthe anode or gun 4. Placed over the anode 4 are the two insulation discsI6 and I'I upon which the two deiiector plates 5 and 6 are supported. Bythe aid of two screws I8 and I9 the entire electrode system is heldtensionally together.

Figure 2 shows another form of ceramic spacer pieces. In this figure theanode and parts of the system surmounting it must be imagined to be 40removed. The two ceramic bodies I 4 and I5, as will be seen, aresupported by the four metallic rods 'I, 8, 2G and 2 I. The two ceramicparts could also be of a form as shown in Figure 3, and this facilitatestheir manufacture to a great extent.

Figures 4 and 5 show another example of the form of the electrodes andthe supporting thereof. I'he electrode 22 has flange-like lugs 23 and 24which have holes 25 and 26 through which the supporting rods 29, 3l!lined with tiny insulation 50 sleeves 2l and 28 are passed. Theelectrode 22 is spaced apart from the next electrode 3| by a smallinsulation tubelet or bushing.

Another simple form of supporting for the electrode system according tothis invention is illustrated in Figure 6. For the sake of clarity ofillustration an exemplified embodiment resembling that in Figure 1 ischosen. The electrodes 34, 35 and 3B are tensionally held between micaplatelets or discs. The latter have holes through which the foursupporter rods 37, 38, 39, 40 are passed. These rods bear insulationsleeves, and arrangements are made so that the insulation sleeves engagethe electrodes from the outside and hold them in position. Spacing isalso here insured by insulation sleeves 4l placed about the supportrods. Since it is comparatively difficult to make the electrodes texactly in the space between the supporting rods, surfaces are providedon the electrodes against which the supporting rods come to bear. Thisis shown by way of example in Figure 8` An electrode 42 is furnishedwith assembly (tting) surfaces 43 and 44. When introducing theelectrodes in their supportings the necessary amount of material can beremoved from these two surfaces for proper t.

Occasionally it is of advantage to make the inner part of the diaphragmin the form of a metallic sheet; this insures sharp edges which will beless liable to be damaged. Metallic diaphragms of this nature, as shownin Figure 9, could be readily combined with the graphite electrodes heredisclosed. For instance, the dia-v graphite, and especially in these theease of working of graphite will be of advantage.

I claim:

1. In a cathode ray tube in which a gun structure is provided forgenerating a beam of elec-Y trons, said gun structurev including acathode, a control electrode and a plurality of. accelerating andfocusing electrodes, one of said last named electrodes comprising acarbon cylindrically shaped member and a pair of centrally perforatedplanar carbon end members, said members being provided withdiametrically opposed unitary extensions, said extensions being providedwith openings parallel with the axis of the cylindrical member, andinsulating means for maintaining said ends of members in contact withthe ends of the cylindrical member with the perforations of the endmembers in alignment with the axis of the cylindrical member.

2. In a cathode ray tube in which a gun structure is provided forgenerating a beam of electrons, said gun structure including a cathode,a control electrode and a plurality of accelerating and focusingelectrodes, one of said last named electrodes comprising a carboncylindrically shaped member and a pair of centrally perforated planarcarbon end members, said members being provided withdiametricallyopposed unitary extensions, said extensions being providedwith openings parallel with the axis of the cylindrical member, anotherof said accelerating electrodes being in the form of a centrallyperforated planar carbon member and insulating means for maintainingsaid end members in contact with the ends of the cylindrical members andsaid other accelerating electrode spaced from one of said end memberswith the perforations of the planar members in alignment with the axisof the cylindrical member.

HEINRICH KNIEPKAMP.

